A phase difference film has been recently widely used for a liquid crystal display as a phase difference control function layer. In a vertically aligned mode liquid crystal display that has been widely applied to a liquid crystal television, in order to reduce viewing angle dependence, a phase difference film (negative C plate) having a negative birefringence anisotropy in which an optical axis is perpendicular to a substrate, and a phase difference film (positive A plate) having a positive birefringence anisotropy in which the optical axis is horizontal to the substrate are simultaneously used.
In the liquid crystal display in which a dark display (dark state) is obtained in a state in which liquid crystal molecules having positive birefringence are aligned perpendicularly to the substrate, no birefringence by alignment of the liquid crystal molecules is caused relative to a normal direction of a display device. Therefore, very high contrast is obtained in the normal direction in the above display devices. However, when the alignment is deviated from the normal direction of the display device, birefringence is caused, and transmittance of the black display (dark state) increases. More specifically, contrast decreases relative to a viewing angle in an oblique direction in the above liquid crystal display devices. The negative C plate can compensate the birefringence to be caused when the liquid crystal alignment is deviated from the normal direction in such a display device. As a result, the negative C plate serves as an optical compensation plate suitable for improving viewing angle characteristics in a vertically aligned (VA), twisted nematic (TN), optically compensated birefringence (OCB) or hybrid aligned nematic (HAN) liquid crystal display.
In addition thereto, many phase difference films such as a viewing angle compensation film in which a discotic liquid crystal is used have been placed on the market. The phase difference films are stacked with any other phase difference plate and a polarizing plate at a specific angle in optical axes with each other, and the resulting stacked material is pasted to an outside of a liquid crystal cell, and thus used. On the occasion, a pressure sensitive adhesive used for lamination is different in a refractive index from the phase difference plate and the polarizing plate, and therefore reflection of outside light is caused in a stacked interface. The outside light reflection reduces the contrast of a display to significantly deteriorate image quality.
Such a problem can be solved by utilizing a liquid crystal material in place of the phase difference film as described above to form a phase difference control function layer in the cell. More specifically, the phase difference control function layer can be arranged using a liquid crystalline polymer that has a glass transition point and can freeze liquid crystal structure thereof at a glass transition temperature or lower, or a polymerizable liquid crystal compound that has a reactive group such as an unsaturated bond in molecular structure thereof and can similarly freeze liquid crystal structure thereof by crosslinking of the unsaturated bond in a liquid crystal layer state. The present inventors have proposed a material described in Patent literature No. 1 as a polymerizable liquid crystal composition that can form the negative C plate.
The polymerizable liquid crystal composition described in Patent literature No. 1 utilizes an optically active compound having a binaphthol moiety and a polymerizable liquid crystal compound having a fluorene skeleton. The polymerizable liquid crystal compositions can be applied in various uses by controlling a kind or an amount of addition of the optically active compound to change a helical pitch of an optically anisotropic substance having twist alignment. The optically anisotropic substance having twist alignment reflects light corresponding to a length of the helical pitch and a direction of rotation of a helix. When the length of the helical pitch is in the range of 380 nanometers to 780 nanometers, visible light is reflected. When the length of the helical pitch is longer than 780 nanometers, near infrared light is reflected, and when the length of the helical pitch is shorter than 380 nanometers, ultraviolet light is reflected. Lamination or pasting of optically anisotropic substances having different directions of rotation allows total reflection. The optically anisotropic substance having such characteristics is referred to as the negative C plate (negative C-plate).